Do youhave labview?

Dear Parthiban,

which is the sampling frequency of your EMG data?

You can figure out the presence of any artifact by looking at the power spectrum of the raw signal. If you are using matlab, there are many functions which allow you to obtain a power spectral estimation. If you want to have a quick look at the frequency content of your signal you can also perform a discrete fourier transform (fft in matlab) and then look at its absolute value. Its plot against a frequency axis will tell you a lot.

Consider filtering the raw EMG data between 20Hz and 450Hz to be sure only the surface EMG useful band is kept, removing any low frequency motion artifact (almost surely located below 20Hz) and high frequency noise. If you have any power line interference, consider removing it by using a notch filter around the power line frequency.

Then, after full wave rectification and low pass filtering you shouldn't have artifacts in your envelope.

For what concerns the units, it could be mV, or it could be quantization levels deriving from the A/D converter, depending on the output file format of your system. Anyway, if you have any reference value (for example a MVC) this is not an issue because you can amplitude normalize your signals. Also, if you are interested in determining on-off instants, units should not be important.

Hi Cristiano and Moataz,

I am a Labview user and having some trouble displaying raw EMG PSD or frequency spectrum data in real-time to search for possible signal noise.... Would either of you have an example .vi that does this that you might be willing to share?

Thanks.

Hi Moataz,

Sorry i don't have Labview.

Hi Jack,

which LabView version are you using? If you have Express VIs, you can find a "spectral" Express VI in the "Signal Analysis" palette with many options for calculating the power spectrum. Then you can simply display it on a graph indicator. Otherwise you should have different VIs in the "signal processing" palette for spectral mesurement applications.

Hi Cristiano,

I am running 2010; but have 2013 (not yet up to installing)... I have the express vis... Works fine with offline analysis; having trouble getting real-time PSD or frequency to display.

Hi Jack,

sorry for the late reply. When i use DAQ assistant to acquire EMG signals via LabView, I usually use express VI power spectrum analysis to have an approximate visual feedback of the spectral content of the signal, by just putting a graph indicator next to the VI. If you acquire within time windows, the analysis will be performed inside those time windows, so you will figure out the presence of any artifact window by window. What kind of noise/artifact are you looking for?

I teach power spectra estimation to my "Biomedical Signal Processing" course students and I applied those technique to EMG in the last 40 years. Just write to to my E-mail (use an internet browser with my name) Bye